Light a large skillet on the stovetop over medium heat. Add bacon to the skillet, and cook until browned and crispy. Remove the bacon from the pan and crumble into small pieces. Set the bacon aside, and reserve the bacon fat.
In a large bowl, combine your bacon fat, spinach, garlic, cream cheese, egg, coconut flour, mozzarella, salt, and pepper. Add 3/4 of the crumbled bacon, saving the rest for the topping.
Fill each mushroom cap with the spinach and cheese mixture and place in a shallow baking dish. Sprinkle the remaining crumbled bacon on top.
Bake 18-20 minutes until golden brown and bubbly. Serve warm.